The present applicant previously proposed in Patent Document 1, Japanese Patent No. 3868630 “an aluminum alloy for a plain bearing having improved fatigue resistance under high surface pressure, characterized in that: it contains 1 to 15% by weight of Sn, 1 to 8% by weight of Si, 0.05 to 0.3% by weight of Cr, and 0.05 to 0.3% by weight of Zr, the balance being Al and unavoidable impurities; it has a annealing temper, namely, a post-rolling annealing comprising a low-temperature annealing at 300 to 400 degrees C. and a high-temperature annealing at 400 to 480 degrees C., with the temperature difference between the low- and high-annealing treatments being 10 degrees C. or more: an Al—Cr intermetallic compound precipitates mainly in the grain boundaries of aluminum, and Al—Zr intermetallic compound precipitates mainly in sub-grains within the crystal grains of the aluminum” (claim 1). In Patent Document 1, the intended use of the aluminum alloy is a plain bearing operated under high surface temperature condition. For this purpose, the structure of the alloy is controlled to have precipitates of the Al—Cr and Al—Zr intermetallic compounds, which contribute to enhancing the fatigue resistance at high temperature. In addition, hard particles formed of Si effectively prevent seizure. Furthermore, Pb and Sn added as optional components also enhance seizure resistance.
In Patent Document 2: Japanese Unexamined Patent Publication (kokai) No. 2007-107589, a resin-based coating layer consisting of a solid lubricant and a resin binder is bonded to aluminum alloy, and cavitation resistance of the coating is improved by means of enhancing bonding strength between the coating layer and aluminum alloy. For this purpose, the Sn content of the aluminum alloy is set in the range of 0 to 2 mass %. The aluminum alloy further contains 0.1 to 20 mass % in total of Si, Cu, Ni, Cr, Zn, Mn, Ti, B, Zr, Mg, V, Pb and/or Bi. Among these elements, the elements other than Si, Pb and Bi (hereinafter referred to as “the elements Si and the like”) are dissolved in the aluminum matrix or form intermetallic compounds with Al to precipitate, according to the descriptions of Patent Document 2. In the Examples, the additive elements are Sn, Cu, Si, Zn, Pb and Mn but not Mg.
The production method disclosed in Patent Document 2 is as follows. An aluminum-alloy cast material is rolled to form an aluminum-alloy sheet, and this sheet is bonded to a steel sheet (backing metal) by means of roll bonding to form a bimetal. Through this process, the elements Si and the like are either dissolved in or caused to precipitate in the aluminum alloy. However, the solution and precipitating conditions are not specifically described. The bimetal is press-worked to have a hemi-cylindrical shape and is then machined to predetermined shapes of parts of interest. A resin coating layer is then provided thereon and baked at 230 to 250 degrees C. for 1 hour in Patent Document 2.
Patent Document 3: Japanese Patent No. 3958515 relates to a multi-layer bearing having a steel backing metal, an aluminum-alloy intermediate layer, and an aluminum-based bearing alloy layer. The aluminum-based bearing alloy layer contains 0.1 to 7 mass % of at least one element selected from Cu, Zn, Mg and Si. The aluminum-based bearing alloy layer, bonded to the steel backing metal, is solution-treated at 400 degrees C. or higher. According to Patent Document 3, the following changes occur during the solution treatment of the aluminum-based bearing alloy layer bonded to the steel backing metal via an intermediate layer. First, such elements as Cu, Zn, Mg and Si of the aluminum based bearing alloy layer are dissolved in the Al matrix and, during subsequent rapid cooling, reinforce the aluminum alloy and hence improve fatigue resistance of a bearing. Incidentally, fatigue resistance is tested at a fed oil temperature of 100 degrees C. An Al—Fe—Si based compound is present in the aluminum-alloy intermediate layer at a side of the backing metal and prevents formation of a brittle Al—Fe based compound. In the Examples, the highest additive amount of Mg in the Al alloy is 1.5%.
Patent Document 3 discloses that the aluminum-based bearing alloy may further contain the elements given below. It is understood that these elements are dissolved in the Al matrix by solution treatment at 400 degrees C. or higher. Alternatively, the aluminum alloy may be subjected to solution treatment and then artificial aging.    (1) 3 to 20 mass % of Sn    (2) 0.1 to 7 mass % in total of one or more elements selected from Cu, Zn, Mg and Si    (3) 0.01 to 3 mass % in total of one or more elements selected from Mn, V, Mo, Cr, Co, Fe, Ni and W    (4) 0.01 to 2 mass % in total of one or more elements selected from B, Ti and Zr    (5) 3 mass % or less in total of one or more elements selected from Pb, Bi and In
Patent Document 4, Japanese Unexamined Patent Publication (kokai) No. 2010-77506 corresponds to a patent application filed earlier than the present application but has not yet been published as of the priority dale of the present application. Patent Document 4 relates to an aluminum alloy for forming an outer panel or the like of the body of an automobile. The aluminum alloy contains 1.5 to 7.0 mass % of Mg, and also contains such elements as Fe, Si, Mn, Cr, Zr, V and Ti as optional components. When Cr and Zr are selected front among them, each of the Cr and Zr contents is 0.3 mass % or less. The production method of an aluminum-alloy rolled sheet described in Patent Document 4 is as follows: homogenizing an ingot; hot rolling (thickness 3.5 mm); cold rolling accompanied with intermediate annealing (thickness 1 mm); solution treatment: and skin pass rolling. Finally, tempering (50-80 degrees C.) is occasionally carried out.